Don't allow spaces in tag names
Don't allow spaces in tag names

This patch restricts the use of spaces in tags, as this does not allow
nice exporting of tags to environment in hooks. One can use underscores
or dashes instead of spaces.

Reviewed-by: schreiberal


ganeti-github-testing/ganeti-test-1,bitemyapp/ganeti,yiannist/ganeti,dimara/ganeti,mbakke/ganeti,andir/ganeti,andir/ganeti,apyrgio/ganeti,apyrgio/snf-ganeti,bitemyapp/ganeti,apyrgio/ganeti,ganeti-github-testing/ganeti-test-1,yiannist/ganeti,mbakke/ganeti,onponomarev/ganeti,leshchevds/ganeti,grnet/snf-ganeti,dimara/ganeti,leshchevds/ganeti,ganeti/ganeti,apyrgio/snf-ganeti,onponomarev/ganeti,mbakke/ganeti,andir/ganeti,yiannist/ganeti,ganeti/ganeti,leshchevds/ganeti,grnet/snf-ganeti,ganeti/ganeti