add version of libflux-security to flux version output

[garlick]

@grondo's commented in #1626

It does feel like maybe we'd want a way outside of compiling a C program to determine if an installed flux-core was built with flux-security support though... maybe we should annotate flux version output with compile time information like some programs do? e.g.

$ flux version --verbose
flux-core-0.9.0
+security
-caliper
or similar?

[garlick]

In #1817, we changed flux-version to report the library, command, and broker version. We should add the security version as discussed in the pr.

[grondo]

Fixed by 30cce87