Limit hostnames to 15 characters (for windows)

[hh]

When trying to use knife-cloud based plugins, the default node name generation is more than 15 characters which gives windows boxes a hard time. This patch limits the names to 15 characters.
/cc @mattray @taylor @vulk

[btm]

Can you expand on the "hard time" part? It would be surprising if old NETBIOS name constraints weren't easily worked around. /cc @opscode/platform-engineering

[mattray]

knife-vcair needs this for Windows to work, there may be work arounds to fix this properly, but this is an edge case that I doubt will get much attention.

[adamedx]

The workaround for netbios limitations is fqdn's -- the DNS name for a Windows system may be long (well, as long as the RFC for DNS names allows I guess). But the legacy "computername" which we think of as hostname has to be less than 16 characters -- typically that computername is the leading component of the DNS name. More here: http://support.microsoft.com/kb/909264.