Echo output when pkg-map fails

When the call to pkg-map fails, it prints the error to stdout. However,
this output is lost when pkg-map is executed in a subshell, so the
actual error is never seen. This change adds an explicit echo so the
error is shown.

Change-Id: Id6f4fae6acadfe2839b408fb2dd11fb65d65df6e
Use readlink to get script path

So we can support usage:
ln -s ~/source/.../disk-image-create ~/bin/

Change-Id: Id54b613a247679b98cef3e9a6f37cd93155d029e
Merge "Echo output when pkg-map fails"
Merge "Use readlink to get script path"