Dockerfile: install git to allow fetching of requirements (#343)

* Dockerfile: install git to allow fetching of requirements
  This was removed by mistake in the docker image compaction PR.
* getos.py: added triplet()

Dockerfile

@@ -69,4 +69,7 @@ RUN	set -e ;\
 	cd /var/opt/redislabs/modules/rg/ ;\
 	ln -s python3 python3_`cat /var/opt/redislabs/artifacts/VERSION`
 
+RUN if [ ! -z $(command -v apt-get) ]; then apt-get -qq update; apt-get -q install -y git; fi
+RUN if [ ! -z $(command -v yum) ]; then yum install -y git; fi
+
 CMD ["--loadmodule", "/var/opt/redislabs/lib/modules/redisgears.so"]

getos.py

@@ -124,6 +124,9 @@ def __init__(self, strict=False):
         elif self.arch == 'armv7l':
             self.arch = 'arm32v7'
 
+    def triplet(self):
+        return '-'.join([self.os, self.osnick, self.arch])
+
     def is_debian_compat(self):
         return self.dist == 'debian' or self.dist == 'ubuntu' or self.dist == 'linuxmint'