Serve OS scripts from metadata daemon
Serve OS scripts from metadata daemon

This patch makes the metadata daemon web server serve the OS scripts
via the instance communication mechanism.  This is achieved by
retrieving the "os" field from the instance parameters and serving the
file directly from the 'Constants.osSearchPath', typically
'/srv/ganeti/os/*/{create,import,export,rename,verify}'.

Signed-off-by: Jose A. Lopes <0fb9c4f8511df4ec2ae28af879e9d462f6218a2c@google.com>
Reviewed-by: Hrvoje Ribicic <be5828fca31f89218048bec4189e30a581aa65da@google.com>

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