[EFW-1790] Additional test, spacing changes, link instead of copy

[kskrzypczyn-arista]

[Investigation] Provide support-diagnostics build in alpine based Barney image

1. Link /mfw-toolchain instead of copy:

• Copying it into tempfs costs us time and increases our memory usage
• entry -> mutates -> mfw-toolchain - linking will cause some mutations to it, not the copy so we need it mutable
• memory: 8Gi -> 4Gi (my last test showed like 3.07 Gi of usage)
• cp -> ln - copy changed to linking

2. test/mfw_pkg/support-diagnostics is using mfw_pkg/support-diagnostics as mount not as base image

• In the build I can add the file support-diagnostics | grep "Python script" check
• test/mfw_pkg/support-diagnostics cache footprint should be lower
• explictly declare no dependency on sources as we now have build key - sources: []

[ut-zuul-app]

Zuul - one or more jobs failed in the check pipeline
https://zuul.infra.corp.arista.io/t/github-untangle-tenant/buildset/2d59c152dad440a68bcd223f8083af63

❌ efw__support-diagnostics__test-mfw-pkg-support-diagnostics efw/support-diagnostics package build failed 🧐, review the job output in 16m 56s
✔️ efw__support-diagnostics__tests-renovate-json5 Renovate.json5 is a valid JSON5 file ☺️ in 2m 14s

Warning:
Dashboard URL for the Zuul buildset: https://dashboard.infra.corp.arista.io/overview?parentJobId=2428595829
For more details on how to track and interpret a zuul build: https://go/zuul-guide

---

efw__support-diagnostics__test-mfw-pkg-support-diagnostics: https://bsy.infra.corp.arista.io/job/J1260108fa3e1dd163e12a2adcd22cae9315b357fb69f838c90ed8199e427d137/status
Image built: code.arista.io/efw/support-diagnostics%test/mfw_pkg/support-diagnostics
Found image called test/mfw_pkg/support-diagnostics defined in barney.yaml at line 46
Error log:

 (3.9.18-1) to root...
Installing python3-light (3.9.18-1) to root...
Installing python3-xml (3.9.18-1) to root...
Installing python3-light (3.9.18-1) to root...
Installing python3 (3.9.18-1) to root...
Installing python3-light (3.9.18-1) to root...
Installing sqlite3-cli (3400000-1) to root...
Installing libsqlite3-0 (3400000-1) to root...
Installing support-diagnostics (local) to root...
Installing python3 (3.9.18-1) to root...
Installing terminfo (6.2-3) to root...
Installing uuidgen (2.36.1-2) to root...
Installing zlib (1.2.11-4) to root...
+ [ build step failed: running [sh -uxec 'mkdir /var/lock
opkg install --force-downgrade /src/support-diagnostics/mfw-packages/*/*

ls /usr/bin/support-diagnostics
file support-diagnostics | grep "Python script"
'] on ref: code.arista.io/efw/build%world: exit status 255 ]
+ [process 0#0] exited with code 255

Full error log: https://bsy.infra.corp.arista.io/job/J12601080867d10cabdff1fb96f41a1dee12bfd60666dbec4acb5efa8e9c9008a/log

[ut-zuul-app]

Zuul - all jobs passed in the check pipeline
https://zuul.infra.corp.arista.io/t/github-untangle-tenant/buildset/4d29441a91dd4e2395589c6aeff57af7

✔️ efw__support-diagnostics__test-mfw-pkg-support-diagnostics efw/support-diagnostics package build successfully ☺️ in 14m 47s
✔️ efw__support-diagnostics__tests-renovate-json5 Renovate.json5 is a valid JSON5 file ☺️ in 2m 17s

Warning:
Dashboard URL for the Zuul buildset: https://dashboard.infra.corp.arista.io/overview?parentJobId=2429771269
For more details on how to track and interpret a zuul build: https://go/zuul-guide