Make sure builds executed locally don't fail (#78)

Fixes #77 
The logic is as follows:
- if build is *not* an RBE build:
  - if platform is Linux:
    - `apt-get install rpm`
  - if platform is Darwin:
    - `brew install rpm`
  - else
    - fail

Author: vmax

ci/install-bazel-rbe.sh

@@ -1,6 +1,22 @@
 #!/bin/bash
 
 set -e
+
+function install_dependencies() {
+    echo "Installing rpmbuild..."
+    if [[ "$OSTYPE" == "linux-gnu" ]]; then
+        sudo apt-get update
+        sudo apt-get install rpm
+    elif [[ "$OSTYPE" == "darwin"* ]]; then
+        brew install rpm
+    else
+        echo "Your platform does not have rpmbuild executable for it. Make sure you are using Linux/macOS".
+        exit 1
+    fi
+}
+
+install_dependencies
+
 echo "Installing RBE credential..."
 if [[ -n "$BAZEL_RBE_CREDENTIAL" ]]; then
     BAZEL_RBE_CREDENTIAL_LOCATION=~/.config/gcloud/application_default_credentials.json