Fix installer to work in JRuby
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 <d95b56ce41a2e1ac4cecdd398defd7414407cc08@causes.com>
Reviewed-by: Shane da Silva <6f6e68d1df92f30cb4b3ce35260ddf94a402f33d@causes.com>

gnagel/overcommit,blech75/overcommit,oxocode/overcommit,TheSooth/overcommit,blech75/overcommit,gnagel/overcommit,oxocode/overcommit,TheSooth/overcommit