Fix build environment and feed configuration in Dockerfile

Dockerfile

@@ -48,9 +48,20 @@ RUN ln -s /usr/bin/automake /usr/bin/automake-1.10 && \
 ENV CONFIG_SHELL=/bin/bash
 
 COPY . /home/builder/openwrt
+
 RUN useradd -m -s /bin/bash builder
+
+RUN cd /home/builder/openwrt && \
+    make -C scripts/config clean && \
+    rm -f scripts/config/zconf.tab.c scripts/config/lex.yy.c && \
+    make -C scripts/config conf
+
+RUN cd /home/builder/openwrt && \
+    wget https://github.com/openwrt/packages/archive/master.tar.gz -O - | tar xz -C feeds/ && \
+    mv feeds/packages-master feeds/packages
+
 RUN chown -R builder:builder /home/builder/openwrt
-RUN git config --system http.sslVerify false
+
 USER builder
 WORKDIR /home/builder/openwrt