* aptly can sign and verify without issues with GnuPG 1.x and 2.x
* aptly auto-detects GnuPG version and adapts accordingly
* aptly automatically finds suitable GnuPG version
Majority of the work was to get unit-tests which can work with GnuPG 1.x & 2.x.
Locally I've verified that aptly supports GnuPG 1.4.x & 2.2.x. Travis CI
environment is based on trusty, so it runs gpg2 tests with GnuPG 2.0.x.
Configuration parameter gpgProvider now supports three values for GnuPG:
* gpg (same as before, default): use GnuPG 1.x if available (checks gpg, gpg1),
otherwise uses GnuPG 2.x; for aptly users who already have GnuPG 1.x
environment (as it was the only supported version) nothing should change; new
users might start with GnuPG 2.x if that's their installed version
* gpg1 looks for GnuPG 1.x only, fails otherwise
* gpg2 looks for GnuPG 2.x only, fails otherwise
These unit-tests cover operations via both PGP providers:
built-in `openpgp` and external `gpg`.
Next step is to run these tests for gpg1 & gpg2
as separate entities.
