Fix test IMS emergency calls using ril.test.emergencynumber

In some situations, testing Emergency Callback Mode using
ril.test.emergencynumber would cause telephony to actually call
emergency services because the test number was not being marked
as emergency correctly.

This change replaces the test emergency number earlier in the
dial so that it is correctly detected as emergency.

Bug: 151861867
Test: manual; Test ECBM over CDMA.
Change-Id: Icba8945acbf9ed55760788354a3cc694bd9e866b