SecureRandom should be thread safe

Random is documented to be thread safe and our implementation appears
to be. However, the SecureRandom subclass implementation was not. This
was quite reproducible with the javax.net.ssl unit tests when run on a
multicore device, but not seen on a uniprocessor.

Details:

   Actual bug fix by adding synchronized to engine* methods

	luni/src/main/java/org/apache/harmony/security/provider/crypto/SHA1PRNG_SecureRandomImpl.java

   New testSecureRandomThreadSafety based on generateSeed errors in javax.net.ssl tests.

	luni/src/test/java/tests/security/SecureRandomTest.java

   Removing dalvik.annotation.* from assorted SecureRandom tests.

	luni/src/test/java/org/apache/harmony/security/tests/java/security/SecureRandom2Test.java
	luni/src/test/java/org/apache/harmony/security/tests/java/security/SecureRandomSpiTest.java
	luni/src/test/java/tests/java/security/SecureRandomTest.java
	luni/src/test/java/tests/security/SecureRandomTest.java

Change-Id: I5e8ece4c0836b02277d7cac1b9b2f60b3c4a7755