Implement test IMS conference event package harness.

Implement test conference event package intent receiver and parser which
allows the user to issue an intent to cause a test conference event
package file to be injected into the current ImsCall:

adb shell am broadcast
-a com.android.internal.telephony.TestConferenceEventPackage
-e filename test_filename.xml

Bug: 18119796
Change-Id: Ic51be9442ae5b991054ccfd7655c6efd76ffd8e0