[TestLldbGdbServer and TestGdbRemoteXXX] Use "ls -l" instead of "readlink"

Summary:
Old Android devices, for example API 16, do not have the "readlink"
command. To take care of such devices, this commit changes to use "ls -l"
instead of "readlink" to get the lldb-server exe path.

The tests fixed with this change for an Android API 16 arm device are:

TestGdbRemoteAttach
TestGdbRemoteAuxvSupport
TestGdbRemoteExpeditedRegisters
TestGdbRemoteKill
TestGdbRemoteProcessInfo
TestGdbRemoteSegFault
TestGdbRemoteThreadsInStopReply
TestGdbRemote_qThreadStopInfo

Further, all tests in TestLldbGdbServer pass (previously erroring out),
except one which times out.

Test Plan:
Run dosep.py with 8 test threads targetting Android API 16
device.

Reviewers: vharron, ovyalov

Reviewed By: ovyalov

Subscribers: tberghammer, aemerson, lldb-commits

Differential Revision: http://reviews.llvm.org/D10107

llvm-svn: 238532