Merge pull request #395 from tracim/feature/upgrade-pbr

install/requirements.txt

 backlash==0.0.7
 beautifulsoup4==4.4.0
 caldav==0.4.0
-cliff==1.8.0
+cliff==2.9.1
 cmd2==0.6.9
 coverage==4.4.1
 crank==0.7.3
 ldap3==1.3.1
 lxml==3.6.0
 nose==1.3.4
-pbr==0.10.0
+pbr==3.1.1
 prettytable==0.7.2
 py4j==0.10.1
 pyasn1==0.1.9