Panic: Handle numeric 3rd party service use of HTTP_EXPOSE or HTTPS_EXPOSE, fixes #2266

[rfay]

The Problem/Issue/Bug:

It is possible to use a numeric value for HTTP_EXPOSE or HTTPS_EXPOSE environment variables in a 3rd-party service.

The code assumes that it will be a string, and crashes with

panic: interface conversion: interface {} is int, not string
goroutine 1 [running]:
github.com/drud/ddev/pkg/ddevapp.(*DdevApp).Describe(0xc00013adc0, 0xc0001c86c0, 0x8, 0x8)
        /workdir/pkg/ddevapp/ddevapp.go:270 +0x31a4
github.com/drud/ddev/cmd/ddev/cmd.glob..func25(0x219d1c0, 0x21d7d90, 0x0, 0x0)
        /workdir/cmd/ddev/cmd/list.go:41 +0x268
github.com/spf13/cobra.(*Command).execute(0x219d1c0, 0x21d7d90, 0x0, 0x0, 0x219d1c0, 0x21d7d90)
        /workdir/vendor/github.com/spf13/cobra/command.go:830 +0x29d
github.com/spf13/cobra.(*Command).ExecuteC(0x219e340, 0x0, 0x0, 0x0)
        /workdir/vendor/github.com/spf13/cobra/command.go:914 +0x2fb
github.com/spf13/cobra.(*Command).Execute(...)
        /workdir/vendor/github.com/spf13/cobra/command.go:864
github.com/drud/ddev/cmd/ddev/cmd.Execute()
        /workdir/cmd/ddev/cmd/root.go:140 +0x3c
main.main()
        /workdir/cmd/ddev/main.go:8 +0x20

This was reported in TYPO3 slack by Elias Häußler, thanks!, https://typo3.slack.com/archives/C8TRNQ601/p1589356915138500

The docker-compose.selenium.yaml that caused this problem is posted at https://gist.github.com/eliashaeussler/df4d277a6c390094436ce2e34783fc3f

How this PR Solves The Problem:

Make sure the environment variable value is a string before using it.

Manual Testing Instructions:

• Install the docker-compose.selenium.yaml above
• ddev start
• ddev describe should work correctly
• ddev list should behave correctly

Workaround for affected users

Just change the affected HTTP_EXPOSE line to

- HTTP_EXPOSE=4444

for example, instead of - HTTP_EXPOSE: 4444

Automated Testing Overview:

Related Issue Link(s):

Release/Deployment notes: