update dockerfiles to fix default branch name in the oracle linux dockerfile and update pip in the centos dockerfile to get back to working order

Dockerfile.centos

@@ -17,7 +17,7 @@ WORKDIR /root
 RUN git clone https://github.com/coreemu/core
 WORKDIR /root/core
 RUN git checkout ${BRANCH}
-RUN ./setup.sh
+RUN ./setup.sh && python3 -m pip install --upgrade pip
 RUN . /root/.bashrc && inv install -v -p ${PREFIX}
 # install emane packages and python bindings
 WORKDIR /root

Dockerfile.oracle

@@ -4,7 +4,7 @@ LABEL Description="CORE Docker Oracle Linux Image"
 
 # define variables
 ARG PREFIX=/usr
-ARG BRANCH=docker-updates
+ARG BRANCH=master
 
 # define environment
 ENV DEBIAN_FRONTEND=noninteractive