Bump version to 1.4.3. Override version in env var
Bump version to 1.4.3. Override version in env var

This commit bumps the default Logstash version to 1.4.3. You can
override the version using the LOGSTASH_VERSION env var.

awyrough/docker-logstash,TaylorMonacelli/docker-logstash-pblittle,pblittle/docker-logstash,eternnoir/docker-logstash,dant3/docker-logstash