cpp: rpc: fixed test dir from environment variable
cpp: rpc: fixed test dir from environment variable

jswrenn/xtreemfs,kleingeist/xtreemfs,jswrenn/xtreemfs,kleingeist/xtreemfs,harnesscloud/xtreemfs,jswrenn/xtreemfs,kleingeist/xtreemfs,kleingeist/xtreemfs,harnesscloud/xtreemfs,kleingeist/xtreemfs,jswrenn/xtreemfs,harnesscloud/xtreemfs,kleingeist/xtreemfs,jswrenn/xtreemfs,kleingeist/xtreemfs,rbaerzib/xtreemfs,rbaerzib/xtreemfs,rbaerzib/xtreemfs,harnesscloud/xtreemfs,rbaerzib/xtreemfs,harnesscloud/xtreemfs,jswrenn/xtreemfs,harnesscloud/xtreemfs,harnesscloud/xtreemfs,jswrenn/xtreemfs,rbaerzib/xtreemfs,rbaerzib/xtreemfs,harnesscloud/xtreemfs,rbaerzib/xtreemfs,jswrenn/xtreemfs,rbaerzib/xtreemfs,kleingeist/xtreemfs