gpg: add 'spack gpg subcommand (#3845)

- Add a `spack gpg` subcommand in anticipation of signed binaries.
- GPG keys are stored in var/spack/gpg, and the spack gpg command manages them.
- Docs are included on the command.

var/spack/gpg.mock/README.md

@@ -0,0 +1,3 @@
+# Mock GPG directory
+
+This directory contains keys and data used in the testing Spack.

var/spack/gpg.mock/data/content.txt

@@ -0,0 +1 @@
+This file has a signature signed by an external key.

var/spack/gpg.mock/data/content.txt.asc

@@ -0,0 +1,17 @@
+-----BEGIN PGP SIGNATURE-----
+Version: GnuPG v2
+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+=kwo9
+-----END PGP SIGNATURE-----

var/spack/gpg.mock/keys/external.key

@@ -0,0 +1,30 @@
+-----BEGIN PGP PUBLIC KEY BLOCK-----
+Version: GnuPG v2
+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+=yVqw
+-----END PGP PUBLIC KEY BLOCK-----

var/spack/gpg/README.md

@@ -0,0 +1,5 @@
+# GPG Keys
+
+This directory contains keys that should be trusted by this installation of
+Spack.  They are imported when running `spack gpg init`, but may also be
+imported manually with `spack gpg trust path/to/key`.