Adapt launchfiles to include single quotes in robot xacro name

[toliver]

Please look at the comments on this PR shadow-robot/sr-ros-interface-ethercat#132

Any plave where we call sr_edc_launch/sr_edc.launch or sr_edc_launch/sr_edc_bimanual.launch should have the single quotes added.

Please think if this can generate additional problems.