flux-broker-attributes.adoc didn't make it into distribution tarball

[grondo]

Not sure exactly why but flux-broker-attributes(7) manpage source didn't make it into the make dist tarball:

> tar tf flux-core-0.4.0.tar.gz  | grep man7
flux-core-0.4.0/doc/man7/
flux-core-0.4.0/doc/man7/Makefile.am
flux-core-0.4.0/doc/man7/Makefile.in
flux-core-0.4.0/doc/man7/COPYRIGHT.adoc

This is causing make install failure when trying to build an RPM:

DEBUG:  /usr/bin/install -c -m 644 ./flux-broker-attributes.7 '/builddir/build/BUILDROOT/flux-core-0.4.0-1.ch5.4.x86_64/opt/flux-core/share/man/man7'
DEBUG: /usr/bin/install: cannot stat `./flux-broker-attributes.7': No such file or directory
DEBUG: make[3]: Leaving directory `/builddir/build/BUILD/flux-core-0.4.0/doc/man7'
DEBUG: make[3]: *** [install-man7] Error 1
DEBUG: make[2]: *** [install-am] Error 2