Add resolution of runtime path using `which` crate

Now it is not required to give complete path of the runtime, if it exists in $PATH
previously needed to provide /usr/bin/run, now only runc resolves to it

youki_integration_test/Cargo.lock

@@ -137,6 +137,12 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "either"
+version = "1.6.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e78d4f1cc4ae33bbfc157ed5d5a5ef3bc29227303d595861deb238fcec4e9457"
+
 [[package]]
 name = "filetime"
 version = "0.2.15"
@@ -514,6 +520,17 @@ version = "0.10.2+wasi-snapshot-preview1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fd6fbd9a79829dd1ad0cc20627bf1ed606756a7f77edff7b66b7064f9cb327c6"
 
+[[package]]
+name = "which"
+version = "4.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ea187a8ef279bc014ec368c27a920da2024d2a711109bfbe3440585d5cf27ad9"
+dependencies = [
+ "either",
+ "lazy_static",
+ "libc",
+]
+
 [[package]]
 name = "winapi"
 version = "0.3.9"
@@ -560,4 +577,5 @@ dependencies = [
  "tar",
  "test_framework",
  "uuid",
+ "which",
 ]

youki_integration_test/Cargo.toml

@@ -21,4 +21,5 @@ test_framework = { version = "0.1.0", path = "../test_framework"}
 anyhow = "1.0"
 lazy_static = "1.4.0"
 once_cell = "1.8.0"
-oci-spec = "0.5.1"
+oci-spec = "0.5.1"
+which = "4.2.2"

youki_integration_test/src/main.rs

@@ -39,8 +39,18 @@ fn parse_tests(tests: &[String]) -> Vec<(&str, Option<Vec<&str>>)> {
 fn main() -> Result<()> {
     let opts: Opts = Opts::parse();
 
-    let path = std::fs::canonicalize(opts.runtime).expect("Invalid runtime path");
-    set_runtime_path(&path);
+    match std::fs::canonicalize(opts.runtime.clone()) {
+        // runtime path is relative or resolved correctly
+        Ok(path) => set_runtime_path(&path),
+        // runtime path is name of program which probably exists in $PATH
+        Err(_) => match which::which(opts.runtime) {
+            Ok(path) => set_runtime_path(&path),
+            Err(e) => {
+                eprintln!("Error in finding runtime : {}\nexiting.", e);
+                std::process::exit(66);
+            }
+        },
+    }
 
     let mut tm = TestManager::new();