Revert "Avoid use of lxml-only getparent()"

This reverts commit 38f55b6257ce51b1cf65ecb3d980d7528c1b53ff.
Client/Frame: avoid use of lxml-only getparent()

getparent is not supported by xml.etree so try to emulate it
with a generated parent_map. This is the only possibility, because
xml.etree does not store references to the parent elements.
Merge branch 'python-pre27-compat' of https://github.com/AlexanderS/bcfg2 into maint
bcfg2.spec: Remove unnecessary lxml dependency

Signed-off-by: Sol Jerome <sol.jerome@gmail.com>