Check for references to ${ROOT} in install_qa_checks.

Check for references to ${ROOT} in install_qa_checks.

When ROOT != /, binaries that reference ROOT will load their
dependencies from ROOT first rather than from the system-configured
path. This is a problem because the ROOT will be / on the target
system.

Besides the above, this patch also fixes incorrect parsing of scanelf
output, where we would treat the RPATHs returned by scanelf as the
names of binaries.

TEST=When "stricter" FEATURE is enabled, verify that emerge
fails when an ebuild references broken rpaths referencing
ROOT. When "stricter" FEATURE is not enabled, verify that such
references are automatically fixed. Also verify that ebuilds
with non-broken RPATHs (e.g. RPATHs referencing $ORIGIN/../lib)
are not touched by the change.

BUG=chromium-os:14271

Change-Id: I4f29cc4ea9195a1255f080284da1f676e4a2c26b

Review URL: http://codereview.chromium.org/6903153