Fix derivation building hanging on gnupg verified fetchurl

[William A. Kennington III]

root@nevada ~/nixpkgs# nix-build -A pkgs.linuxPackages_latest.kernel.srcVerified
download-from-binary-cache.pl: could not download ‘https://cache.triton.wak.io/nix-cache-info’ (Curl error 6)
these derivations will be built:
  /nix/store/hlwajsj48fm5pbqspqpq0ynnz9sqj8v5-linux-4.6.3.tar.xz.drv
building path(s) ‘/nix/store/r3954q356vym2zr2asli4j4mdn0my554-linux-4.6.3.tar.xz’
dirmngr[12419.0]: error opening '/tmp/nix-build-linux-4.6.3.tar.xz.drv-0/ldapservers.conf': No such file or directory
dirmngr[12420.0]: can't access directory '/nix/store/sdggf67p4q428dfbi0ncs4rafdnfknxa-gnupg-2.1.13/etc/gnupg/trusted-certs': No such file or directory
dirmngr[12420.0]: can't access directory '/nix/store/sdggf67p4q428dfbi0ncs4rafdnfknxa-gnupg-2.1.13/etc/gnupg/extra-certs': No such file or directory
dirmngr[12420.0]: permanently loaded certificates: 0
dirmngr[12420.0]:     runtime cached certificates: 0
dirmngr[12420.0]: failed to open cache dir file '/tmp/nix-build-linux-4.6.3.tar.xz.drv-0/crls.d/DIR.txt': No such file or directory
dirmngr[12420.0]: creating directory '/tmp/nix-build-linux-4.6.3.tar.xz.drv-0/crls.d'
dirmngr[12420.0]: new cache dir file '/tmp/nix-build-linux-4.6.3.tar.xz.drv-0/crls.d/DIR.txt' created
gpg: directory '/tmp/nix-build-linux-4.6.3.tar.xz.drv-0/.gnupg' created
gpg: new configuration file '/tmp/nix-build-linux-4.6.3.tar.xz.drv-0/.gnupg/dirmngr.conf' created
gpg: new configuration file '/tmp/nix-build-linux-4.6.3.tar.xz.drv-0/.gnupg/gpg.conf' created
gpg: keybox '/tmp/nix-build-linux-4.6.3.tar.xz.drv-0/.gnupg/pubring.kbx' created
gpg: no running Dirmngr - starting '/nix/store/sdggf67p4q428dfbi0ncs4rafdnfknxa-gnupg-2.1.13/bin/dirmngr'
gpg: waiting for the dirmngr to come up ... (5s)
gpg: connection to the dirmngr established
gpg: data source: http://pgp.mit.edu:11371
gpg: armor header: Version: SKS 1.1.5
gpg: armor header: Comment: Hostname: pgp.mit.edu
gpg: armor header: Version: SKS 1.1.5
gpg: armor header: Comment: Hostname: pgp.mit.edu
gpg: pub  rsa2048/79BE3E4300411886 2011-09-20  Linus Torvalds <[e-mail]>
gpg: /tmp/nix-build-linux-4.6.3.tar.xz.drv-0/.gnupg/trustdb.gpg: trustdb created
gpg: using pgp trust model
gpg: key 79BE3E4300411886: public key "Linus Torvalds <[e-mail]>" imported
gpg: no running gpg-agent - starting '/nix/store/sdggf67p4q428dfbi0ncs4rafdnfknxa-gnupg-2.1.13/bin/gpg-agent'
gpg: waiting for the agent to come up ... (5s)
gpg: connection to agent established
gpg: pub  rsa4096/38DBBDC86092693E 2011-09-23  Greg Kroah-Hartman (Linux kernel stable release signing key) <[e-mail]>
gpg: key 38DBBDC86092693E: public key "Greg Kroah-Hartman (Linux kernel stable release signing key) <[e-mail]>" imported
gpg: 0 keys processed (0 validity counts cleared)
gpg: no ultimately trusted keys found
gpg: Total number processed: 2
gpg:               imported: 2
hi
hi
Trying https://www.kernel.org/pub/linux/kernel/v4.x/linux-4.6.3.tar.sign
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   819  100   819    0     0   8857      0 --:--:-- --:--:-- --:--:--  8902

trying https://www.kernel.org/pub/linux/kernel/v4.x/linux-4.6.3.tar.xz
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 85.3M  100 85.3M    0     0  28.1M      0  0:00:03  0:00:03 --:--:-- 28.1M
gpg: Signature made Fri Jun 24 17:22:46 2016 UTC using RSA key ID 38DBBDC86092693E
gpg: Good signature from "Greg Kroah-Hartman (Linux kernel stable release signing key) <[e-mail]>" [unknown]
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: 647F 2865 4894 E3BD 4571  99BE 38DB BDC8 6092 693E