tidy up install-dependencies script a bit to be more obvious/verbose about usage

PROJECT should be community or nova, not enterprise

Print out usage message when BUILD_TYPE is not provided or one of the supported values.

Author: craigcomstock

build-scripts/install-dependencies

@@ -14,11 +14,12 @@
 #
 # ^ When building community you won't need enterprise, nova.
 #
-# The script can be run as follows:
-# ```
-# $ PROJECT=[enterprise|community] EXPLICIT_ROLE=[hub|agent] BUILD_TYPE=[DEBUG|RELEASE] ./buildscripts/build-scripts/install-dependencies
-# ```
-#
+# The script can be run as described in the usage message below:
+
+function usage() {
+  echo "Usage: PROJECT=[nova|community] EXPLICIT_ROLE=[hub|agent] BUILD_TYPE=[DEBUG|RELEASE] $0"
+  exit 0
+}
 
 . "$(dirname "$0")"/functions
 . detect-environment
@@ -155,7 +156,9 @@ for dep in $DEPS; do
         tests=yes
         ;;
     *)
-        fatal "Unknown build type: $BUILD_TYPE"
+        log_error "Unknown build type: $BUILD_TYPE"
+        usage
+        exit 1
         ;;
     esac