Catch missing python modules and print message (#2221)

* Add `python-requirements` target for main Sming Makefile to install core requirements

* Catch missing optional python modules and print more obvious message

Sming/Components/Storage/Tools/hwconfig/config.py

@@ -5,7 +5,13 @@
 import os, partition, storage
 from common import *
 from builtins import classmethod
-from rjsmin import jsmin
+
+try:
+    from rjsmin import jsmin
+except ImportError as err:
+    sys.stderr.write("\n** %s: please run `make python-requirements` **\n\n" % str(err))
+    sys.exit(1)
+
 
 def findConfig(name):
     dirs = os.environ['HWCONFIG_DIRS'].split(' ')

Sming/Makefile

@@ -175,6 +175,14 @@ $(CLEAN_TESTS):
 
 ##@Tools
 
+CACHE_VARS += PIP_ARGS
+PIP_ARGS ?=
+.PHONY: python-requirements
+python-requirements: ##Install Python requirements for framework via pip (use PIP_ARGS=... for additional options)
+	@echo Installing Python requirements...
+	$(Q) $(PYTHON) -m pip install $(PIP_ARGS) -r $(SMING_HOME)/../Tools/requirements.txt
+
+
 # Recursive wildcard search
 # $1 -> list of directories
 # $2 -> file extensions filters (using % as wildcard)