Fix quotations marks in exported variable

In new catkin versions exported variables are partly enclosed in single quotes instead of double quotes. That means that the variable must not contain single quotes, even when preceded by backslash. This fixed the error `Syntax error: redirection unexpected` during the catkin build process

generate_environment_variables.py

@@ -19,10 +19,10 @@ def parse_arguments():
     return args
 
 MAVEN_HEADER="""
-	<settings xmlns='http://maven.apache.org/SETTINGS/1.0.0/'
-    xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
-    xsi:schemaLocation='http://maven.apache.org/SETTINGS/1.0.0
-    http://maven.apache.org/xsd/settings-1.0.0.xsd'>
+	<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0/"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0
+    http://maven.apache.org/xsd/settings-1.0.0.xsd">
 		<profiles>
 			<profile>
 				<id>catkin</id>
@@ -144,6 +144,6 @@ if __name__ == '__main__':
         print(home)
     elif args.create_maven_settings:
         s = (MAVEN_HEADER + get_repositories_xml() + MAVEN_FOOTER)
-        print(repr(s)[1:-1].replace("'", "\\'"))
+        print(repr(s)[1:-1])
     else:
         print("Nothing to see here - please provide one of the valid command switches.")