Add gnupg "keyboxd" workaround

Author: tianon

Dockerfile-builder.template

@@ -53,7 +53,7 @@ RUN set -eux; \
 #       Key fingerprint = AB07 D806 D2CE 741F B886  EE50 B025 BA8B 59C3 6319
 # uid                  Peter Korsgaard <jacmet@uclibc.org>
 # sub   2048g/45428075 2009-01-15
-RUN gpg --batch --keyserver keyserver.ubuntu.com --recv-keys AB07D806D2CE741FB886EE50B025BA8B59C36319
+RUN mkdir -p ~/.gnupg && gpg --batch --keyserver keyserver.ubuntu.com --recv-keys AB07D806D2CE741FB886EE50B025BA8B59C36319
 
 # https://buildroot.org/download.html
 # https://buildroot.org/downloads/?C=M;O=D
@@ -222,7 +222,7 @@ ENV PATH /usr/src/buildroot/output/host/usr/bin:$PATH
 #       Key fingerprint = C9E9 416F 76E6 10DB D09D  040F 47B7 0C55 ACC9 965B
 # uid                  Denis Vlasenko <vda.linux@googlemail.com>
 # sub   1024g/2C766641 2006-12-12
-RUN gpg --batch --keyserver keyserver.ubuntu.com --recv-keys C9E9416F76E610DBD09D040F47B70C55ACC9965B
+RUN mkdir -p ~/.gnupg && gpg --batch --keyserver keyserver.ubuntu.com --recv-keys C9E9416F76E610DBD09D040F47B70C55ACC9965B
 
 # https://busybox.net: {{ .date }}
 ENV BUSYBOX_VERSION {{ .version }}