Fix attach when running as root without sysfsutils

When someone runs nova as root, and sysfsutils is not installed
an exception was being thrown when a volume attach call was made.
This wouldn't happen when being run as non-root because of the
rootwrap would trap for the missing sysfsutils app (systool).

Change-Id: Icc852fa7fd7a137cc7df86b8b96aeb629639ffad
Fixes: bug 1172486
(cherry picked from commit 001961ed495a33cc944407888a2797f8a600e091)
Convert the cache key from unicode to a string.

The memcached API expects string format, not unicode.
Convert the key passed to the memory cache to a string
before sending it to memcached. Since both the function
name and the id that form the key are ascii format, a
simple conversion from unicode to str is sufficient.

Change-Id: I9d15858ad4e10aa183444cccda9c33676059e55a
Fixes: bug #1174487
(cherry picked from commit 37fbfad813e12d00da8f9d3e9f6f13256d5bb7c1)
Merge "Convert the cache key from unicode to a string." into stable/grizzly
Merge "Fix attach when running as root without sysfsutils" into stable/grizzly