UCS/SYS: Fix loading UCS modules for executable file with dot in name

[dmitrygx]

What

This patch fixes loading UCS modules for executable fileы with dot in name.

Why ?

If some executable file contains . in the name (e.g. ".py" in case python file with UCX bindings), UCX assumes that it is file extension name (like ".so" or ".dll") and changes default module_ext value from ".so" to parsed value. It leads to the case that UCX modules can't be loaded.

How ?

1. Remove code that searches . in the name of executable file and update module_ext value.
2. Define share library file extension through shrext from configure.ac.

[yosefe]

does it happen when UCS is linked statically into another module?

[dmitrygx]

does it happen when UCS is linked statically into another module?

no, it happens with dynamically loaded libraries (aka modules), but when an executable file has . in its name, e.g. ucx_perftest.py

[dmitrygx]

@yosefe @brminich could you merge pls? CLA has already been signed. Thanks!