Switch to use_stdin=True by default in LSFCluster

[lesteve]

This was discussed in #360 (comment), and other places for example #328 (comment).

The summary is:

• use_stdin=False does bsub job_script rather than bsub < job_script
• use_stdin=False was decided based on using dask-jobqueue on Summit (part of Rewrite dask-jobqueue with SpecCluster #307). This does not seem to be representative of other LSF clusters.
• at one point, we thought this was related to LSF 10 but actually not since bsub < job_script is mentioned in https://www.ibm.com/support/knowledgecenter/en/SSWRJV_10.1.0/lsf_command_ref/bsub.zz1argument.command.1.html (search for "bsub <" to find the exact place it is mentioned)