[Fixes #373] Fixed envsubst not working on Ubuntu18.04/CentOS8 on VirtualBox

[anvithks]

What type of PR is this?
/kind bug fix

What this PR does / why we need it:
This PR fixes the issue of dashboard not accessible on fresh installation on Ubuntu18.04 and CentOS8 on VirtualBox.
During the process of bringing up the docker container for dashboard the entrypoint.sh file is executed. As part of the initialisation the nginx configuration and environment variable substitution is performed.
This environment variable substitution is performed using the following line: link here
envsubst '\${OPENSDS_S3_HOST} \${OPENSDS_S3_PORT}' < "/var/www/html/assets/data/runtime.json" > "/var/www/html/assets/data/runtime.json"

This code works on Ubuntu 16.04 and Ubuntu 18.04 when installing on a VM or a Laptop. But while installing on VirtualBox using Ubuntu18.04 or CentOS8 the above line does not execute.
The envsubst command is shipped with the nginx:alpine image on which the docker container for the dashboard is based and is the recommended way to replace environment variables at runtime.

To solve this issue the line is replaced with the following line:
echo "{\"hostIP\": \"$OPENSDS_S3_HOST\",\"hostPort\": \"$OPENSDS_S3_PORT\"}" >/var/www/html/assets/data/runtime.json

Which issue(s) this PR fixes:

Fixes #373

Test Report Added?:
/kind TESTED

Test Report:

Special notes for your reviewer:
Tested on VirtualBox installation of Ubuntu18.04. Able to access the dashboard.

[kumarashit]

LGTM

[skdwriting]

LGTM