Install bash in alpine based images.

This fix https://github.com/Mailu/Mailu/issues/918

Bash shell is used by default in Kubernetes' dashboard console, which is very
useful for admins.

core/admin/Dockerfile

@@ -1,7 +1,7 @@
 FROM alpine:3.8
 # python3 shared with most images
 RUN apk add --no-cache \
-    python3 py3-pip git \
+    python3 py3-pip git bash \
   && pip3 install --upgrade pip
 RUN pip3 install git+https://github.com/usrpro/MailuStart.git#egg=mailustart
 # Image specific layers under this line

core/dovecot/Dockerfile

@@ -1,7 +1,7 @@
 FROM alpine:3.8
 # python3 shared with most images
 RUN apk add --no-cache \
-    python3 py3-pip git \
+    python3 py3-pip git bash \
   && pip3 install --upgrade pip
 # Shared layer between rspamd, postfix, dovecot, unbound and nginx
 RUN pip3 install git+https://github.com/usrpro/MailuStart.git#egg=mailustart

core/nginx/Dockerfile

@@ -1,7 +1,7 @@
 FROM alpine:3.8
 # python3 shared with most images
 RUN apk add --no-cache \
-    python3 py3-pip git \
+    python3 py3-pip git bash \
   && pip3 install --upgrade pip
 # Shared layer between rspamd, postfix, dovecot, unbound and nginx
 RUN pip3 install git+https://github.com/usrpro/MailuStart.git#egg=mailustart

core/postfix/Dockerfile

@@ -1,7 +1,7 @@
 FROM alpine:3.8
 # python3 shared with most images
 RUN apk add --no-cache \
-    python3 py3-pip git \
+    python3 py3-pip git bash \
   && pip3 install --upgrade pip
 # Shared layer between rspamd, postfix, dovecot, unbound and nginx
 RUN pip3 install git+https://github.com/usrpro/MailuStart.git#egg=mailustart

optional/clamav/Dockerfile

@@ -1,7 +1,7 @@
 FROM alpine:3.8
 # python3 shared with most images
 RUN apk add --no-cache \
-    python3 py3-pip \
+    python3 py3-pip bash \
   && pip3 install --upgrade pip
 # Image specific layers under this line
 RUN apk add --no-cache clamav rsyslog wget clamav-libunrar

optional/postgresql/Dockerfile

@@ -1,7 +1,7 @@
 FROM alpine:3.8
 # python3 shared with most images
 RUN apk add --no-cache \
-    python3 py3-pip \
+    python3 py3-pip bash \
   && pip3 install --upgrade pip
 # Shared layer between rspamd, postfix, dovecot, unbound and nginx
 RUN pip3 install jinja2

optional/radicale/Dockerfile

@@ -1,7 +1,7 @@
 FROM alpine:edge
 
 RUN echo "@testing http://nl.alpinelinux.org/alpine/edge/testing" >> /etc/apk/repositories \
- && apk add --no-cache radicale@testing py-dulwich@testing curl
+ && apk add --no-cache radicale@testing py-dulwich@testing curl bash
 
 COPY radicale.conf /radicale.conf
 

services/fetchmail/Dockerfile

@@ -1,7 +1,7 @@
 FROM alpine:3.8
 # python3 shared with most images
 RUN apk add --no-cache \
-    python3 py3-pip \
+    python3 py3-pip bash \
   && pip3 install --upgrade pip
 # Image specific layers under this line
 RUN apk add --no-cache fetchmail ca-certificates \

services/rspamd/Dockerfile

@@ -1,7 +1,7 @@
 FROM alpine:3.8
 # python3 shared with most images
 RUN apk add --no-cache \
-    python3 py3-pip git \
+    python3 py3-pip git bash \
   && pip3 install --upgrade pip
 # Shared layer between rspamd, postfix, dovecot, unbound and nginx
 RUN pip3 install git+https://github.com/usrpro/MailuStart.git#egg=mailustart

services/unbound/Dockerfile

@@ -1,7 +1,7 @@
 FROM alpine:3.8
 # python3 shared with most images
 RUN apk add --no-cache \
-    python3 py3-pip git \
+    python3 py3-pip git bash \
   && pip3 install --upgrade pip
 # Shared layer between rspamd, postfix, dovecot, unbound and nginx
 RUN pip3 install git+https://github.com/usrpro/MailuStart.git#egg=mailustart