solver: gracefully handle cache loading errors

[tonistiigi]

fix #1468

Signed-off-by: Tonis Tiigi [email protected]

[tonistiigi]

@AkihiroSuda v0.7?

[ebeuker]

i am also having the same issue in an azure devops pipeline.. however i am using a custom build of buildctl that contains the pr solver: gracefully handle cache loading errors #1498. My buildctl is based on commit 929fff0

my pipeline is inspired by this setup: https://dev.azure.com/codesharing-SU0/cachesandbox/_git/Scripts?path=%2Fdocker.yml&version=GBmaster

i extended it to do a second build to execute the unit tests:
sudo buildctl build --frontend=dockerfile.v0 --local context=./src/ --local dockerfile=. --import-cache type=local,src=$(BUILD_KIT_CACHE) --opt target=test-results --output type=local,dest=$(System.DefaultWorkingDirectory)/out

this build fails about 60% of the time