adt_installer: Fix sed file not found error

We need to look for the installed file within the sysroot we just installed
so add in the missing prefix. This avoids errors like:

Installing cross canadian packages for qemux86 ...
sed: no input files

[YOCTO #6443]

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
python3: fix builtins imports

The intent of this code is to generate things like -L=/usr/lib/foo so
for paths which start with "/" we should appent the "=". We should not do this
for ".". On some recent versions of binutils or patchsets on some recent
distros this appears to work differently and causes build failures, for example
on Ubuntu 14.04 LTS.

The simple fix is to check for "." as the path prefix.

[YOCTO #6467].

Signed-off-by: Roxana <roxana.ciobanu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>