Further debugging support

[thesamesam]

Following on from #7, I think we still need to do a bit more for debugging.

In https://forums.gentoo.org/viewtopic-p-8804931.html, I've been trying to help a user debug their stuck sync, but the current --debug output gives:

$ emerge --sync --debug
myopts {'--debug': True, '--regex-search-auto': 'y'}
[DEBUG] Using selector: EpollSelector
>>> Syncing repository 'gentoo' into '/var/db/repos/gentoo'...
[DEBUG] Using selector: EpollSelector
 * Using keys from /usr/share/openpgp-keys/gentoo-release.asc
 * Refreshing keys via WKD ...[DEBUG] list_keys(): keyid: A13D0EF1914E7A72
[DEBUG] list_keys(): fingerprint: EF9538C9E8E64311A52CDEDFA13D0EF1914E7A72
[DEBUG] list_keys(): UID: [[email protected]](mailto:[email protected])
[DEBUG] list_keys(): keyid: DB6B8C1F96D8BF6D
[DEBUG] list_keys(): fingerprint: DCD05B71EAB94199527F44ACDB6B8C1F96D8BF6D
[DEBUG] list_keys(): UID: [[email protected]](mailto:[email protected])
[DEBUG] list_keys(): ignoring UID without mail: b'Gentoo Portage Snapshot Signing Key (Automated Signing Key)'
[DEBUG] list_keys(): keyid: 9E6438C817072058
[DEBUG] list_keys(): fingerprint: D99EAC7379A850BCE47DA5F29E6438C817072058
[DEBUG] list_keys(): UID: [[email protected]](mailto:[email protected])
[DEBUG] list_keys(): keyid: BB572E0E2D182910
[DEBUG] list_keys(): fingerprint: 13EBBDBEDE7A12775DFDB1BABB572E0E2D182910
[DEBUG] list_keys(): UID: [[email protected]](mailto:[email protected])
[DEBUG] Starting new HTTPS connection (1): gentoo.org:443 # <-- hangs here

I think we really need some way to easily get that dirmngr output as mentioned in #7 (comment).

Interestingly, in the past, we used to do some of this unconditionally but it was removed in 2f8b327 but the commit message isn't clear as to why.

[mgorny]

No clue offhand. FWICS --debug-all implies all of the following:

gpg: available debug flags:
gpg:      1 packet
gpg:      2 mpi
gpg:      4 crypto
gpg:      8 filter
gpg:     16 iobuf
gpg:     32 memory
gpg:     64 cache
gpg:    128 memstat
gpg:    256 trust
gpg:    512 hashing
gpg:   1024 ipc
gpg:   4096 clock
gpg:   8192 lookup
gpg:  16384 extprog