Fix installer to work in JRuby

JRuby's implementation of `File.symlink?` raises an exception when the
file does not exist, which is different from the default MRI
implementation.

Fix by returning false when that exception is thrown.

Change-Id: I2672acdc265e29e8af1531d4e05293367558dc82
Reviewed-on: http://gerrit.causes.com/35998
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>
Ignore SignalException Rubocop check

This convention doesn't seem necessary.

Change-Id: I443032acba887e4bd0856219af1be37b74c5d9eb
Reviewed-on: http://gerrit.causes.com/35999
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>