Refactor handling of Composer to be version based

More in line with how a provisioning script should handle things. If the expected version of Composer is not installed, either install it or update to that version. If the expected version is installed, don't waste time looking for the update.

provision/provision.sh

@@ -193,18 +193,19 @@ ln -fs /usr/bin/ack-grep /usr/bin/ack
 
 # COMPOSER
 #
-# Install Composer
-if [ ! -f /home/vagrant/flags/disable_composer ]
+# Install or Update Composer based on expected hash from repository
+if composer --version | grep -q 'Composer version e4b48d39d';
 then
-	if [ ! -f /usr/local/bin/composer ]
-	then
-		printf "Install Composer...\n"
-		curl -sS https://getcomposer.org/installer | php
-		chmod +x composer.phar
-		mv composer.phar /usr/local/bin/composer
-	else
-		printf "composer already installed\n"
-	fi
+	printf "Composer already installed\n"
+elif composer --version | grep -q 'Composer version';
+then
+	printf "Updating Composer version\n"
+	composer self-update
+else
+	printf "Install Composer...\n"
+	curl -sS https://getcomposer.org/installer | php
+	chmod +x composer.phar
+	mv composer.phar /usr/local/bin/composer
 fi
 
 # If our global composer sources don't exist, set them up