Fix list_merge_keys target for gpg2
Fix list_merge_keys target for gpg2

The output from `gpg --list-keys --with-colons` has changed between gpg
version 1.4 and 2.

1.4:

$ gpg --list-keys --with-colons 14491C3B34141441
tru::1:1472766925:1549885469:3:1:5
pub:f:2048:1:14491C3B34141441:2012-09-03:::-:Alex Tomlins <alex.tomlins@digital.cabinet-office.gov.uk>::scESC:
sub:f:2048:1:59F1AEBB3A532D3C:2012-09-03::::::e:

2.0:

$ gpg --list-keys --with-colons 14491C3B34141441
tru::1:1472807696:1473327764:3:1:5
pub:u:2048:1:14491C3B34141441:1346678456:::u:::scESC:
uid:u::::1346678456::BE7B1C9571B9C159A1FFFF170F999708841F51FA::Alex Tomlins <alex.tomlins@digital.cabinet-office.gov.uk>:
sub:u:2048:1:59F1AEBB3A532D3C:1346678456::::::e:

This updates the awk script to detect the gpg version, and when it's gpg
2, look at the uid element in the results. Additionally, since there may
be more than one uid for a given key, it now exits after outputting the
first one.

alphagov/paas-cf,alphagov/paas-cf,jimconner/paas-cf,jimconner/paas-cf,jimconner/paas-cf,jimconner/paas-cf,alphagov/paas-cf,jimconner/paas-cf,jimconner/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,jimconner/paas-cf