Purge ssh-auth key cache after trust/untrust

Summary: See PHI358. The `bin/almanac [un]trust-key` workflows don't properly purge the SSH key cache, but should.

Test Plan:
  - Added key `ssh-rsa xyz` to a device.
  - Used `bin/ssh-auth | grep xyz` to test for the presence of the key.
  - Before patch: Saw it not present, trusted it, saw it still not present.
  - After patch: Saw it not present, trusted it, saw it now present. Untrusted it, saw it no longer present.

Differential Revision: https://secure.phabricator.com/D19053

src/applications/almanac/management/AlmanacManagementTrustKeyWorkflow.php

@@ -81,6 +81,8 @@ final class AlmanacManagementTrustKeyWorkflow
     $key->setIsTrusted(1);
     $key->save();
 
+    PhabricatorAuthSSHKeyQuery::deleteSSHKeyCache();
+
     $console->writeOut(
       "**<bg:green> %s </bg>** %s\n",
       pht('TRUSTED'),

src/applications/almanac/management/AlmanacManagementUntrustKeyWorkflow.php

@@ -43,6 +43,8 @@ final class AlmanacManagementUntrustKeyWorkflow
     $key->setIsTrusted(0);
     $key->save();
 
+    PhabricatorAuthSSHKeyQuery::deleteSSHKeyCache();
+
     $console->writeOut(
       "**<bg:green> %s </bg>** %s\n",
       pht('TRUST REVOKED'),