largefiles: avoid redundant changectx looking up at each repetitions
These code paths look up changectx at each repetitions, even though
the changectx key isn't changed while loop.
FROM fedora:21
RUN yum install -y gcc
RUN yum install -y python-devel python-docutils
RUN yum install -y make
RUN yum install -y rpm-build
RUN yum install -y gettext
# For creating repo meta data
RUN yum install -y createrepo