add support for outputting a Semver compatible build version
add support for outputting a Semver compatible build version

Currently we pass the git describe output straight through as the build
version.  This makes it difficult to parse the package name since it
does not follow any package/version naming convention.  This commit adds
a new `server` method which produces a Semver compatible build
version.

jamesn/omnibus,szechyjs/omnibus,Scalr/omnibus,chef/omnibus,jamesn/omnibus,intfrr/omnibus,3ofcoins/chef-omnibus,mattray/omnibus,servebox/omnibus,Scalr/omnibus,strangelittlemonkey/omnibus,sh9189/omnibus,Altiscale/omnibus,DataDog/omnibus-ruby,Scalr/omnibus,3ofcoins/chef-omnibus,intfrr/omnibus,adamleff/omnibus,rapid7/omnibus,ashhher3/omnibus,higanworks/omnibus,lvfeng1130/omnibus,intfrr/omnibus,3ofcoins/chef-omnibus,servebox/omnibus,servebox/omnibus,pskrz/omnibus,Altiscale/omnibus,rapid7/omnibus,hugosato/omnibus,strangelittlemonkey/omnibus,pskrz/omnibus,ashhher3/omnibus,DataDog/omnibus-ruby,jamesn/omnibus,chef/omnibus,lvfeng1130/omnibus,hugosato/omnibus,adamleff/omnibus,chef/omnibus,higanworks/omnibus,rhass/omnibus,lvfeng1130/omnibus,sh9189/omnibus,mattray/omnibus,adamleff/omnibus,szechyjs/omnibus,rapid7/omnibus,hugosato/omnibus,DataDog/omnibus-ruby,strangelittlemonkey/omnibus,sh9189/omnibus,higanworks/omnibus,pskrz/omnibus,Altiscale/omnibus,ashhher3/omnibus,szechyjs/omnibus,rhass/omnibus,rhass/omnibus,mattray/omnibus