[Cherry-Pick] Read/use Directory Transport version from Skopeo

[asmacdo]

Adds comparators for a new class Version which represents a skopeo
directory transport version. This will allow us to easily support
future changes.

containers/image#419
fixes: #3703

[pep8speaks]

Hello @asmacdo! Thanks for submitting the PR.

• In the file common/pulp_docker/common/dir_transport.py, following are the PEP8 issues :

Line 5:80: E501 line too long (97 > 79 characters)
Line 40:80: E501 line too long (91 > 79 characters)

• In the file common/test/unit/test_dir_transport.py, following are the PEP8 issues :

Line 23:80: E501 line too long (87 > 79 characters)
Line 32:80: E501 line too long (91 > 79 characters)

• In the file plugins/pulp_docker/plugins/importers/upload.py, following are the PEP8 issues :

Line 2:80: E501 line too long (97 > 79 characters)
Line 5:80: E501 line too long (95 > 79 characters)
Line 6:80: E501 line too long (81 > 79 characters)
Line 14:80: E501 line too long (98 > 79 characters)
Line 47:80: E501 line too long (92 > 79 characters)
Line 49:80: E501 line too long (96 > 79 characters)
Line 63:80: E501 line too long (80 > 79 characters)
Line 72:80: E501 line too long (85 > 79 characters)
Line 95:80: E501 line too long (83 > 79 characters)
Line 96:80: E501 line too long (84 > 79 characters)
Line 113:80: E501 line too long (84 > 79 characters)
Line 126:80: E501 line too long (96 > 79 characters)
Line 146:80: E501 line too long (98 > 79 characters)
Line 151:80: E501 line too long (81 > 79 characters)
Line 173:80: E501 line too long (93 > 79 characters)
Line 176:80: E501 line too long (98 > 79 characters)
Line 191:80: E501 line too long (91 > 79 characters)
Line 197:80: E501 line too long (85 > 79 characters)
Line 204:80: E501 line too long (87 > 79 characters)
Line 217:80: E501 line too long (80 > 79 characters)
Line 221:80: E501 line too long (81 > 79 characters)
Line 225:80: E501 line too long (88 > 79 characters)
Line 239:80: E501 line too long (87 > 79 characters)
Line 241:80: E501 line too long (86 > 79 characters)
Line 249:80: E501 line too long (100 > 79 characters)
Line 280:80: E501 line too long (80 > 79 characters)
Line 294:80: E501 line too long (99 > 79 characters)
Line 307:80: E501 line too long (89 > 79 characters)
Line 308:80: E501 line too long (86 > 79 characters)
Line 310:80: E501 line too long (83 > 79 characters)
Line 348:80: E501 line too long (89 > 79 characters)
Line 351:80: E501 line too long (93 > 79 characters)
Line 353:80: E501 line too long (91 > 79 characters)
Line 356:80: E501 line too long (80 > 79 characters)
Line 360:80: E501 line too long (89 > 79 characters)
Line 363:80: E501 line too long (82 > 79 characters)
Line 367:80: E501 line too long (92 > 79 characters)
Line 369:80: E501 line too long (93 > 79 characters)
Line 371:80: E501 line too long (88 > 79 characters)
Line 374:80: E501 line too long (80 > 79 characters)
Line 387:80: E501 line too long (80 > 79 characters)
Line 395:80: E501 line too long (96 > 79 characters)
Line 405:80: E501 line too long (91 > 79 characters)
Line 418:80: E501 line too long (82 > 79 characters)
Line 441:80: E501 line too long (91 > 79 characters)

• In the file plugins/test/unit/plugins/importers/test_upload.py, following are the PEP8 issues :

Line 2:80: E501 line too long (95 > 79 characters)
Line 28:80: E501 line too long (83 > 79 characters)
Line 29:80: E501 line too long (82 > 79 characters)
Line 78:80: E501 line too long (83 > 79 characters)
Line 79:80: E501 line too long (91 > 79 characters)
Line 163:80: E501 line too long (83 > 79 characters)
Line 164:80: E501 line too long (88 > 79 characters)
Line 196:80: E501 line too long (83 > 79 characters)
Line 197:80: E501 line too long (89 > 79 characters)
Line 233:80: E501 line too long (83 > 79 characters)
Line 236:80: E501 line too long (91 > 79 characters)
Line 240:80: E501 line too long (90 > 79 characters)
Line 258:80: E501 line too long (83 > 79 characters)
Line 259:80: E501 line too long (96 > 79 characters)
Line 274:80: E501 line too long (99 > 79 characters)
Line 307:80: E501 line too long (80 > 79 characters)

[ipanova]

lgtm