removed unused imports
First import of the ARCComputingElement
Do not use md5 sum checking by default between SE service and client
If ExecTime < CPUTime then ExecTime=CPUTime for accounting
Added discovery of ARC pilot reference
Use CE name in the pilot reference url construction
Use SSHHost to retrieve job output
Use token keyword
Make CheckSum a possible option of a storage protocol, default is yes
Merge pull request #1563 from atsareg/fix-v6r7

[v6r7] Several fixes
v6r7p38 notes
Take into account that Ports can be a list in the SE definition
Allow grid environment script with arguments
After debugging
Merge pull request #1571 from atsareg/fix-v6r7

[v6r7] Several fixes
v6r7p39
v6r8p24 notes
Conflicts resolved after merging with rel-v6r7