Change each test profile running only its category

Previously, "long" test profile would run tests of "unit", "short"
and "long" categories. After this change, each profile only runs its
own category.

Author: avelanarius

CONTRIBUTING.md

@@ -89,7 +89,7 @@ The Maven build uses profiles named after the categories to choose which tests t
 mvn test -Pshort
 ```
 
-The default is "unit". Each profile runs the ones before it ("short" runs unit, etc.)
+The default is "unit". Each profile runs only their own category ("short" will *not* run "unit").
 
 Integration tests use [CCM](https://github.com/pcmanus/ccm) to bootstrap Cassandra instances.
 Two Maven properties control its execution:

pom.xml

@@ -951,31 +951,31 @@
         <profile>
             <id>short</id>
             <properties>
-                <test.groups>unit,short</test.groups>
+                <test.groups>short</test.groups>
                 <test.osgi.skip>false</test.osgi.skip>
             </properties>
         </profile>
 
         <profile>
             <id>long</id>
             <properties>
-                <test.groups>unit,short,long</test.groups>
+                <test.groups>long</test.groups>
                 <test.osgi.skip>false</test.osgi.skip>
             </properties>
         </profile>
 
         <profile>
             <id>duration</id>
             <properties>
-                <test.groups>unit,short,long,duration</test.groups>
+                <test.groups>duration</test.groups>
                 <test.osgi.skip>false</test.osgi.skip>
             </properties>
         </profile>
 
         <profile>
             <id>doc</id>
             <properties>
-                <test.groups>unit,doc</test.groups>
+                <test.groups>doc</test.groups>
             </properties>
         </profile>