podman logs: fix tailing

Fix issues with tailing of container logs as described
in issue #16.  Also add in the ability to use a duration or
known time stamp formats for the --since flag.

Signed-off-by: baude <bbaude@redhat.com>

Closes: #317
Approved by: mheon

vendor/github.com/hpcloud/tail/tail_posix.go

@@ -1,11 +0,0 @@
-// +build linux darwin freebsd netbsd openbsd
-
-package tail
-
-import (
-	"os"
-)
-
-func OpenFile(name string) (file *os.File, err error) {
-	return os.Open(name)
-}