Fix DSA APK signatures for API Level 8 and lower.

This modifies JAR signing code to produce DSA signatures which are
accepted by all Android platforms rather than only API Level 9 and
higher.

The issue is that by default Bouncy Castle uses OID 1.2.840.10040.4.3
(dsaWithSha1) in PKCS #7 CMS SignerInfo whereas Android accepts that
only since API Level 9. However, OID 1.2.840.10040.4.1 (dsa) is
accepted by all Android platforms.

Bug: 27461702
Change-Id: I24256a255bcdc2108bdb447557af7568a2c096e3