[test] Correctly retry connections on android targets

Summary:
Normally, when the remote stub is not ready, we will get ECONNREFUSED during the connect()
attempt. However, due to the way how ADB forwarding works, on android targets the connect() will
always be successful, but the connection will be immediately dropped if ADB could not connect on
the remote side. This commit tries to detect this situation, and report it as "connection
refused" so that the upper test layers attempt the connection again.

Reviewers: tfiala, tberghammer

Subscribers: tberghammer, danalbert, srhines, lldb-commits

Differential Revision: http://reviews.llvm.org/D18146

llvm-svn: 263439