Bug: delete_module() syscall might get interrupted under load.

Bug: delete_module() syscall might get interrupted under load.

staprun might fail to delete modules and leave ko in the system:

  $ sudo lsmod|grep stap
  stap_2eb3039808b647e990825b99fb1f9b6_18830   221184  0
  stap_eee9b566240fbeb1194347a571ccd68_17219   208896  0

Now we try up to 5 times for the delete_module() syscall in staprun with
a growing sleep interval between successive attempts upon the EINTR
error.