better git tag deployment support

[ldarren]

changes:

• check ref is a branch or a tag
• fixed deployment error due to "forced-pushed" branch
• added an optional branch option, to support deployment git tag to a different name

old command

pm2 deploy config.json production ref tags/prod-v1.0.0

# resulting a new branch named "prod-v1.0.0" on production server, which causing git warning about same tag and branch name

new command

pm2 deploy config.json production ref tags/prod-v1.0.0 v1.0.0

# resulting a new branch named "v1.0.0" on production server, no more git warning