staprun: interpret a non-zero systemtap_module_init() return as an error

staprun: interpret a non-zero systemtap_module_init() return as an error

Errors returned from systemtap_module_init() can often be positive, and
tracking down all sources of the positive return values is error-prone.
Instead, simply interpret any non-zero return from systemtap_module_init()
as an error so that staprun doesn't poll forever on waiting for a dead
stap module to do something.