Use de::CommandLine in execserver
Use de::CommandLine in execserver

Using de::CommandLine provides better command line argument parsing and
improved diagnostics in case of failures.

Change-Id: I4685ef84f17171cfe3fd4d6a99f84dbb55c64b18

maurossi/deqp,chadversary/deqp,maurossi/deqp,googlestadia/VK-GL-CTS,chadversary/deqp,geekboxzone/mmallow_external_deqp,KhronosGroup/Vulkan-CTS,geekboxzone/mmallow_external_deqp,chadversary/deqp,KhronosGroup/Vulkan-CTS,chadversary/deqp,maurossi/deqp,KhronosGroup/VK-GL-CTS,KhronosGroup/VK-GL-CTS,maurossi/deqp,KhronosGroup/Vulkan-CTS,KhronosGroup/VK-GL-CTS,maurossi/deqp,KhronosGroup/Vulkan-CTS,googlestadia/VK-GL-CTS,geekboxzone/mmallow_external_deqp,KhronosGroup/Vulkan-CTS,maurossi/deqp,geekboxzone/mmallow_external_deqp,googlestadia/VK-GL-CTS,googlestadia/VK-GL-CTS,googlestadia/VK-GL-CTS,KhronosGroup/VK-GL-CTS,KhronosGroup/VK-GL-CTS,geekboxzone/mmallow_external_deqp,geekboxzone/mmallow_external_deqp,KhronosGroup/VK-GL-CTS,chadversary/deqp,chadversary/deqp,googlestadia/VK-GL-CTS,KhronosGroup/Vulkan-CTS