fix(amazonlinux): epel does not exist in amazonlinux, so we make it c…

…onditional

Dockerfile.yum

@@ -12,7 +12,7 @@ ARG EXTRA_PACKAGES=""
 ARG PKGS="udev git net-tools sudo curl openssh-server openssh-clients which $EXTRA_PACKAGES"
 
 # Centos 7 and 6 requires EPEL repo before being able to install python2-pip
-RUN [ "$DISTRO_NAME" = "centos" ] && yum -y install epel-release
+RUN if [ "$DISTRO_NAME" = "centos" ]; then yum -y install epel-release; fi
 RUN yum -y update && yum -y install ${PKGS}
 
 # The sed command is a quick fix for https://github.com/saltstack/salt-bootstrap/issues/1371