Fix use of relative paths in Scripts/*/*.sh

Most scripts (e.g. Keystone.sh) assume that they are being started
from their parent directory. This is is not a safe assumption,
especially considering that even test_scripts.sh calls them
from _its_ parent directory (e.g. bash Keystone/Keystone.sh).

This patch introduces a SCRIPT_DIR variable and inserts it wherever
relative paths are used.

Change-Id: Id2ff690e9d4e961dba8aebb8871668e2c6d2dccd
Keep Glance.sh from using the Internet

The scripts running after PreInstall.sh are supposed to work without
an Internet connection ("Internet connection is not required for this
script to run").

However, Glance.sh tried to wget the CirrOS disk image which cannot
work in an offline environment. This patch moves the download into
PreInstall.sh. Also, update CirrOS image from 0.3.1 to 0.3.2.

Change-Id: Ibefbffdda1591ed4561a67edda8a50f17c14aae5
Merge "Fix use of relative paths in Scripts/*/*.sh"
Merge "Keep Glance.sh from using the Internet"