Remove duplicated code to create policies and templates.

Factor out the code to create ESP policies and templates to two
new methods that can be used both by the socket policy tests and
the tunnel tests.

All the policy and template code are now in these methods in
xfrm_base.

Bug: 70371070
Bug: 63589535
Test: all xfrm tests pass on android-4.9
Change-Id: Iec0c5a1eb78ddc56908485e5ea62a671569c1dcc