Nag when ANDROID_HOME is undefined

[jsotuyod]

Since the last changes to support newer AGP versions, we use the ANDROID_HOME env var

static-code-analysis-plugin/src/main/groovy/com/monits/gradle/sca/AndroidHelper.groovy

Lines 136 to 142 in 406b9d8

	/**
	* Retrieves the current Android SDK install location
	* @return The current Android SDK install location
	*/
	static String getSdkDir() {
	System.getenv('ANDROID_HOME')
	}

We should complain to the user if we find this to be undefined / invalid