Alter container/pod/volume name regexp to match Docker

Docker's upstream name validation regex has two major differences
from ours that we pick up in this PR.

The first requires that the first character of a name is a letter
or number, not a special character.

The second allows periods in names.

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

libpod/options.go

@@ -17,7 +17,7 @@ import (
 )
 
 var (
-	nameRegex = regexp.MustCompile("[a-zA-Z0-9_-]+")
+	nameRegex = regexp.MustCompile("^[a-zA-Z0-9][a-zA-Z0-9_.-]*$")
 )
 
 // Runtime Creation Options