Replace utils.ensure_(str|unicode) with strutils.safe(decode|encode)

Glanceclient implemented both functions before they landed into oslo.
Since both functions are already in oslo, it is now possible to pull
them in.

There's a small difference between glance's implementation and oslo's,
that is the later does not convert non-str objects - int, bool - to str
before trying to decode / encode them. This patch takes care of that
where necessary, more precisely, while encoding headers before doing a
new request.

Fixes bug: #1172253

Change-Id: I9a0dca31140bae28d8ec6aede515c5bb852b701b

openstack-common.conf

@@ -1,7 +1,9 @@
 [DEFAULT]
 
 # The list of modules to copy from openstack-common
+module=gettextutils
 module=importutils
+module=strutils
 
 # The base module to hold the copy of openstack.common
 base=glanceclient