Remove org.apache.http.legacy from bootclasspath

Updates the tests to work when org.apache.http.legacy is no longer on the
bootclasspath.

1) Added new test to verify that org.apache.http.legacy is added to the
   classpath for an APK that is targeted at an earlier release (27) that makes
   the org.apache.http.legacy classes available on the bootclasspath.

2) Added <uses-library android:name="org.apache.http.legacy"/> to the
   CtsApacheHttpLegacyCurrentApiSignatureTestCases' AndroidManifest.xml file so
   that it can see the classes.

3) Made sure that the org.apache.http.legacy classes are not available by
   default.

Test: cts/tests/signature/runSignatureTests.sh
Bug: 18027885
Change-Id: I4bfa352a67b31906d49a587a5c5e580c44a6e8bc
9 files changed