handle missing lib gracefully

[2501babe]

if you provide an incorrect value to --library, the cli ignores it and runs cargo build-sbf at the toplevel. but then at the end it tries to use the library to locate the elf file to hash. the cli prints "Error: Failed to parse output" and exits. in practice what this has meant is thinking "did it fail? huh, no seems like it worked. yay!" and then a month later realizing you have five running docker containers 😅

instead, print a helpful message and continue to docker kill

(incidentally the reason it printed "Failed to parse output" instead of "Failed to find program" is because find x -name y outputs nothing and returns 0 if y doesnt exist. it will however return 1 if x doesnt exist)

[2501babe]

oh i see #205 handles this the opposite way, i assumed the --library flag was ignored on purpose. if you merge that pr then close this one, or vice versa

[char23-web]

git clone https://github.com/Ellipsis-Labs/solana-verifiable-build.git
cd solana-verifiable-build

[swaroop-osec]

Closing as #205 was merged